Room air conditioning units are often mounted in openings in the outer walls of buildings and are left in place throughout the year. Such through the wall units must be mounted so that they can be replaced when necessary; in a typical installation, the unit rests within a metal sleeve or frame mounted around the wall opening, with the sleeve usually extending an inch or two from the wall into the interior of the room. An air conditioning unit can be replaced by simply sliding it out of the metal sleeve and sliding a new unit in place. Where an air conditioning unit is not desired by the occupant of the apartment, the wall opening can be closed off, typically by fitting a box-like metal cap over the ends of the sleeve on the interior and exterior sides of the wall.
In colder climates, the through the wall air conditioning units can be a major source of heat loss from a building during the winter months. The air conditioner unit itself is not air tight and can allow cold outside air to pass through into the room interior. In addition, since the air conditioner sits loosely within the sleeve which surrounds it, cold air can blow through the areas between the sleeve and the air conditioner, and sometimes between the sleeve and the adjacent wall structure, resulting in a substantial heat loss from the apartment. Weatherstripping placed between the air conditioner and the sleeve can be helpful but does not totally eliminate seepage of cold air into the room between the sleeve and the air conditioner, and does nothing to prevent heat loss through the air conditioner itself. This heat loss has prompted apartment dwellers to attempt to cover the air conditioner with plastic sheet material or blankets, remedies which are both unsightly and largely ineffective. With rising energy costs, the lost heat due to the air conditioner openings requires attention on the part of landlords, but the only reasonably effective solution has been to remove the air conditioner each fall and to fill and cover the wall opening--operations which are time consuming and expensive. Air leaks still occur even about the openings that have been filled and capped because there are often cracks between the sleeve and the wall and because the seal between the cap and the sleeve is generally not air-tight.